10 ZOOLOGY. 



16. Chemical Composition of Protoplasm. It is impossible to make 

 a satisfactory chemical analysis of protoplasm, as it loses its characteristic 

 powers and probably undergoes important chemical and physical changes 

 in the act of analysis. The dead material thus obtained is no longer the 

 substance with which we started, either as to its power or its structure. 

 The experiment shows however that the substance is both chemically and 

 physically unstable. By an analysis of the dead protoplasm, we find pres- 

 ent several complex organic compounds, known as proteids, carbohydrates 

 (starches and sugars), fats, ferments, pigments, etc. In addition to these 

 are simpler inorganic compounds, as water and various salts. Doubtless 

 some of these materials are food-substances on their way to form proto- 

 plasm, and others are the waste-products of protoplasmic disruption, ready 

 to be cast out of the cell. The proteids are the most complex of all these 

 substances and it is believed that protoplasm finds- its real basis in these. 



The proteids are various in composition and properties, but agree in 

 that their molecules contain carbon, hydrogen, oxygen, nitrogen, and sul- 

 phur, in proportion roughly as follows : C 53%, O 22%, N 17%, H 

 7%, S i%. The white of egg, the fibrin of the blood, and casein in milk 

 are examples of proteid. 



Carbohydrates consist of C, H, and O. The latter elements are always 

 present in the ratio in which they are represented in water (H 2 O), e. g. 

 CeHioCX The starches, sugars, and cotton fibres are illustrations. 



The fats contain the same elements as starch, but the percentage of 

 oxygen in terms of the hydrogen is much smaller than in the starches. 



The ferments are complex organic substances which have the power of 

 producing important chemical changes in other substances without being 

 themselves consumed. They play an important, but not thoroughly un- 

 derstood, role in the activities of the organisms, both within and outside 

 the cells which produce them. The active principle of the digestive juices, 

 as ptyalin and pepsin, are examples of ferments which have been extruded 

 from the cells. 



Water (H 2 O) is very important in both the chemical and physical 

 structure of protoplasm. It is very variable in amount, and the degree 

 of activity of the protoplasm is roughly proportional to the amount of 

 water present. Traces of inorganic salts, compounds of chlorine, potas- 

 sium, sodium, calcium, phosphorus, iron, etc., are als6 found in solution 

 in the water. 



17. The Physical Structure of Protoplasm. This varies 

 much from time to time. On account of differences in the 

 amount of water present, the consistency of protoplasm may 

 vary from the quite fluid condition found in actively growing 

 parts, to the very much more solid condition apparent in dry 

 seeds and in the resting or encysted stage of some animals. 

 In these latter instances the protoplasm eliminates a large per 



